78 lines
1.9 KiB
Go
78 lines
1.9 KiB
Go
package randx
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import (
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crand "crypto/rand"
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"encoding/hex"
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"io"
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)
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// Bytes returns n cryptographically secure random bytes.
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func Bytes(n int) ([]byte, error) {
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if n <= 0 {
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return []byte{}, nil
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}
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b := make([]byte, n)
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_, err := io.ReadFull(crand.Reader, b)
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return b, err
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}
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var urlSafe = []byte("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_")
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// String returns a URL-safe random string of length n using a cryptographically secure source.
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func String(n int) (string, error) {
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if n <= 0 {
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return "", nil
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}
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out := make([]byte, n)
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// rejection sampling to avoid modulo bias
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// we want uniform selection from urlSafe (len m)
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m := len(urlSafe)
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threshold := 256 - (256 % m)
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var buf [1]byte
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for i := 0; i < n; i++ {
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for {
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if _, err := io.ReadFull(crand.Reader, buf[:]); err != nil {
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return "", err
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}
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b := int(buf[0])
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if b < threshold {
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out[i] = urlSafe[b%m]
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break
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}
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}
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}
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return string(out), nil
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}
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// MustString is like String but panics on error.
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func MustString(n int) string {
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s, err := String(n)
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if err != nil {
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panic(err)
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}
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return s
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}
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// UUIDv4 generates a RFC 4122 version 4 UUID string.
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func UUIDv4() (string, error) {
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b := make([]byte, 16)
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if _, err := io.ReadFull(crand.Reader, b); err != nil {
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return "", err
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}
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// Set version (4) and variant (10)
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b[6] = (b[6] & 0x0f) | 0x40
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b[8] = (b[8] & 0x3f) | 0x80
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// Format 8-4-4-4-12
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dst := make([]byte, 36)
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hex.Encode(dst[0:8], b[0:4])
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dst[8] = '-'
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hex.Encode(dst[9:13], b[4:6])
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dst[13] = '-'
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hex.Encode(dst[14:18], b[6:8])
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dst[18] = '-'
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hex.Encode(dst[19:23], b[8:10])
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dst[23] = '-'
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hex.Encode(dst[24:36], b[10:16])
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return string(dst), nil
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}
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